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Effects of 24R,25-Dihydroxyvitamin D3 on gamma-glutamyl transpeptidase and alkaline
phosphatase activities in Rat Brains.
F. Darcy, L. Sindji, J.C. Peter, E. Garcion, A. Girault, Mustayeen A. Khan, P. Brachet, X.T. Do.
To cite this version:
F. Darcy, L. Sindji, J.C. Peter, E. Garcion, A. Girault, et al.. Effects of 24R,25-Dihydroxyvitamin
D3 on gamma-glutamyl transpeptidase and alkaline phosphatase activities in Rat Brains.. Vitamin
D, A Pluripotent Steroid Hormone-9th Workshop on Vitamin D, May 1994, Orlando, Florida, United
States. �hal-03193532�
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EFFECTS OF 24R,25-DIHYDROXYVITAMIN Dg ON 1'GLUTAMYL- TRANSPEPTIDASE NNO ALKALINE PHOSPHATASE ACTIVITIES IN
RAT BRAINS
F.
DARCY*, L.SINDJI*, J.C. PETER'*, E.GARCION-, A.G
IRAULT**, M.A.KHAN***, P.BRACHET* and X.T.DO**, Unit6 INSERM 298* and Laboratoire de Biochimie- M6decine/Pharmacie*", CHU, Chimie de Coordination-Pharmacie**., F-49100 Angers, France.
lntroduction. yGlutamyl transpeptidase (GGT) and alkaline phosphatase (AP) are two marker enzymes 6t tn. oiooo-orain barrier (BBB) which plays a major role in
the control of brain homeostasis. Do et at. (1) have recently demonstrated that iirtrapeiltoneal (lP) injections of z41,z}-dihydroxyvitamin Ds t24'25-{AH)e Ds) induce an increase in GGT and AP activities in rat kidneys. lt was then of interest to-investigate whether these enzymatic activities could also be modified in rat
brains bivitamin Ds metabolites. ln addition to the effects ol 24,25-(OH)z Ds, already demonstrated in the kidney, we are also
-studying those of
.1,25-(OH)z Ds' considered as the biologically active metabolite. Since rat enzymatic aclivities are more elevated during night than during day (2), the experiments were carried out throughout the night Period.
Materials and Methods. Female Sprague-Dawley r{s (250 t 30 g) were conditioned for 3 weeks before experiments at 20 t 2 oC in arlificial lighting from 8.00 a.m. to 8.00 p.m. and in darkness during the remaining period. six animals per series received at various times during the night a single lP injection ol 24,25' iOHi" Ds, 1,25-(OH)z Dg or vehicle alone (control rats). Brains were. removed {rom 6.00 a.m. to 8.00 a.m., when enzyme activities are maximum, then homogeneized in a potter device. After centrifugation at 2000 g for 20 min., the activities of GGT
(GGt kit, Boehringer) and of AR 1fn=yline kii,.Biom6rieux) were tested in the supernatants toget[ei with the protein concentration (Bio-Rad Laboratories)'
Resuhs and Discussion. ln preliminary experiments, rat brains were collected 6
hafter the lP ',r1"ct'on of various doses of z.+,zs-1OU)z Ds (from 5 to 100 nglg.b'w')' Whereas the lower doses stimulated GGT and AP activities, the highest doses displayed inhibitory properties. Further experiments were carried out with the physiological dose of 10 ng/g.b.w.
Kinetic studies showed tnit za,zs-(oH)z Dg induces in brain a constant increase in GGT activity from 2 h to 5 h, with a maximum of 67 "/" al5 h (Fig' 1A), and a
diphasic increise in AP activity (Fig. 1B). ln contrast to that observed in the kidney
1d1,
Z+,ZS-(OH)z Ds stimulatesin the brain more intensely GGT than AP activity' inirr.rtingiy, tne lp injection of 10 ng/g.b.w. of 1,25-(OH)z Ds inducedJirst a sharp increase iup to 140 % at 3 h) followed by a decrease (-67 % and -77 % at 8 h
and 24 ni ii Cef cerebral activity. Although these.data need to be confirmed by
additional experiments, they suggest a down-regulation of GGT activity induced
by 1,25-(OU;i Os. ln contrasi, AP ictivity was conitantly enhanced from 3 h to 6 h'
641
reaching its maximum level (50%) at 4 h, and then returned to its basal level.
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Figure 1: Kinetic effects o124,25-(OH)z Ds on GGT (A) and AP (B) activities in rat brains (Student'st-test: * p< 0.05, *,. p < 0.01).
These resutts clearly demonstrate that both 24,25-(OH)z Ds and 1,25-(OH)zDs are aclive on cerebral GGT and AP activities. This is of particular interest in the case of GGT, likely involved in the aminoacid transport through the BBB (a). ln addition,
the action of 1,25-(OH)z Ds on the central nervous system (CNS) has been recently evidenced by in vitro (5) and in vivo (6) studies. Considering that both GGT and 1,25-(OH)z Ds could be involved in the physiopathology of the CNS, their interrelationships should be further investigated.
Acknowledgments. We wish to thank Drs Schneider, Weber and Fischer (Hoffmann-Laroche, Basel,switzerland) for their kind gift of vitamin D metabolites, and C. Fandard, R. Breget and P. Planchenault for excellent technical assistance.
References.
1-Do, T.X., Prelot, M., Planchenault, P. and Girault,A. (1991), ln vitamin D, gene regulation, structure-function analysis and clinical application, pp 310-311, W. de Gruyter, Berlin, New York
2-Do, T.X., Boisnard, P., Girault, A., Planchenault, p., Breget, R. and prelot, M.
(1992), Sci.Tech.Anim.Lab., 17, 2OT-211.
3-Do, T.X., Peter, J.C., Girault, A., Rabjeau,A., Bouet, G., Sindji, L. and Darcy, F.
(1994), 9th Workshop on Vitamin D, Orlando, Florida (abstract).
4-Cardelli-Cangiano, P., Fiori, A., Cangiano, C., Barberini, F., Allegra, p.,
Peresempio, V. and Strom, R. (1987), J.Neurochem.,49, 1667-1675.
S-Naveilhan, P., Neveu, 1., Baudet, C., Ohyama, K.Y., Brachet, p. and Wion, D.
(1
993), Neurorepo ft, 5, 255-257.
6-Saporito, M.S., Wilcox, H.M., Hartpence, K.C., Lewis, M.E., Vaught, J.t-. and Carswell., S.
(1993), Exp.Neurol., 123, 295-302.
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